1. Field of the Invention
The present invention relates to an antireflection film and an optical element coated with the antireflection film, and particularly to an antireflection film coated on the surface of an optical element comprising quartz as a substrate, the antireflection film having an antireflection effect in two wavelength regions of ultraviolet light having a wavelength of 248 nm, for example, KrF excimer laser beam, and light having a wavelength of 633 nm, which is visible light, for example, He-Ne laser beam.
2. Related Background Art
As conventional anti-reflection films for two wavelength regions, the first being a region of ultraviolet light having a wavelength of 300 nm or shorter and the second being a region of visible light, films utilizing an oxide film and a fluoride film are disclosed in Japanese Patent Publication Nos. 7-7124 and 7-107563. Anti-reflection films having a film structure of six layers using an oxide film are disclosed in Japanese Patent Application Laid-Open No. 7-218701.
In the above-described conventional cases, however, the use of the fluoride film has created a problem in that low environmental resistance of this film easily degrades performance. On the other hand, the film having a structure in which only the oxide film, which is excellent in environmental resistance, is used has narrow bandwidth.
It is an object of the present invention to solve the above-described problems and provide a high-performance antireflection film having good antireflection characteristics in two wavelength regions of ultraviolet light having a wavelength of 248 nm and visible light having a wavelength of 633 nm and excellent durability, and an optical element coated with the antireflection film.
Another object of the present invention is to provide an antireflection film comprising an alternately multi-layered film of 10 layers formed on a base member and having antireflection characteristics in two wavelength regions including a first wavelength (xcex1) of 248 nm and a second wavelength (xcex2) of 633 nm as central wavelengths, respectively, the multi-layered film of 10 layers comprising:
low-refractive index layers arranged at odd-numbered positions from a side opposite to the base member and having a refractive index of 1.45 to 1.52 at the first wavelength (xcex1); and
high-refractive index layers arranged at even-numbered positions from the side opposite to the base member and having a refractive index of 1.65 to 1.80 at the first wavelength (xcex1),
wherein layers arranged at the first, second and third positions from the side opposite to the base member each have an optical thickness ranging from 0.21xcex1 to 0.28xcex1.
Still another object of the present invention is to provide an optical element comprising:
a base member; and
an antireflection film comprising an alternately multi-layered film of 10 layers formed on the base member and having antireflection characteristics in two wavelength regions including a first wavelength (xcex1) of 248 nm and a second wavelength, (xcex2) of 633 nm as central wavelengths, respectively, wherein the multi-layered film of 10 layers comprises:
low-refractive index layers arranged at odd-numbered positions from a side opposite to the base member and having a refractive index of 1.45 to 1.52 at the first wavelength (xcex1); and
high-refractive index layers arranged at even-numbered positions from the side opposite to the base member and having a refractive index of 1.65 to 1.80 at the first wavelength (xcex1), and
wherein layers arranged at the first, second and third positions from the side opposite to the base member each have an optical thickness ranging from 0.21xcex1 to 0.28xcex1.
A further object of the present invention is to provide an antireflection film comprising an alternately multi-layered film of 8 layers formed on a base member and having antireflection characteristics in two wavelength regions including a first wavelength (xcex1) of 248 nm and a second wavelength (xcex2) of 633 nm as central wavelengths, respectively, the multi-layered film of 8 layers comprising:
low-refractive index layers arranged at odd-numbered positions from a side opposite to the base member and having a refractive index of 1.45 to 1.52 at the first wavelength (xcex1); and
high-refractive index layers arranged at even-numbered positions from the side opposite to the base member and having a refractive index of 1.65 to 1.80 at the first wavelength (xcex1),
wherein layers arranged at the first, second and third positions from the side opposite to the base member each have an optical thickness ranging from 0.23xcex1 to 0.28xcex1.
A still further object of the present invention is to provide an optical element comprising:
a base member; and
an antireflection film comprising an alternately multi-layered film of 8 layers formed on the base member and having antireflection characteristics in two wavelength regions including a first wavelength (xcex1) of 248 nm and a second wavelength (xcex2) of 633 nm as central wavelengths, respectively, wherein the multi-layered film of 8 layers comprises:
low-refractive index layers arranged at odd-numbered positions from a side opposite to the base member and having a refractive index of 1.45 to 1.52 at the first wavelength (xcex1); and
high-refractive index layers arranged at even-numbered positions from the side opposite side to the base member and having a refractive index of 1.65 to 1.80 at the first wavelength (xcex1), and
wherein layers arranged at the first, second and third positions from the side opposite to the base member each have an optical thickness ranging from 0.23xcex1 to 0.28xcex1.